Something like a childhood bully falls for the girl he teased. The bullied girl transfer out and then they meet again. He falls for her and he doesn't know it was the girl he teased long time ago.

Something like that. If anyone knows, please tell me.

An example is: Kimi no Sei

It can also be childhood bully meets the girl he bullied. He likes her when they were childhood friends. She meets him and didn't know that he was the one who bullied her. She later finds out and freaks out.

MIUNOHRI TO SWAN by Hwang Mi Ri. (It just started so there's nothing much in there right now. It's a manwa though, not a manga.)
HE'S DEDICATED TO ROSES also by Hwang Mi Ri (Girl is bullied by guy who actually likes her. But that's not the main story.)
GOKUJOU TWINS by Shiiba Nana (Pretty close to what you're looking for.)
ORESAMA TEACHER by Tsubaki Izumi (At the start, Girl didn't know that her teacher was the neighbor who used to bully her.)
FLY HIGH! by Oouchi Natsumi (Not sure if bully will fall for the bullied.)
IT'S LOVE by Pack Sang Eun (Step brothers bully girl but actually likes her.)
FIRST LOVE (ARUKO) by Aruko (One day, Haruka got confessed by a guy. That guy is none other than Konno, the one who bullies her around when they were kids, and now he's telling her that he liked her since the first time they met. Please read the rest of the summary on Manga Fox.)
HONEY HONEY BOY - HE IS A SWEET TEMPTATION by Shinjo Mayu(Guy bullies girl but actually likes her.)
ASA MO, HIRU MO, YORU MO by Aoki Kotomi (Boy looks like the one who tormented girl appears, then he confesses)
6th Megane by Kaiya Tatsumi (Boy love. Cute story.)
They aren't all exactly as the story you described but they have the bully falls for bullied thing. Read them on Manga Fox. I've seen others but I can't remember the titles.